The desire to maintain a youthful appearance by preventing or reducing wrinkles in the skin is an important issue in human society. Many techniques have been designed to achieve the above issue. One of the techniques known from the published international patent application WO 2008/001284 A2 is to create a focal spot in a dermis layer of the skin to be treated. Said WO application discloses a skin treatment device with a laser source and focusing optics, wherein the power of the laser is selected such that Laser Induced Optical Breakdown (LIOB) affects the skin in order to stimulate re-growth of skin tissue and reduce wrinkles. This LIOB is based on strong non-linear absorption of the laser light by the skin tissue, which occurs above a certain threshold value of the power density of the laser light in the focal spot of the laser beam. This strong absorption causes a localized plasma that is able to damage or even remove tissue at the location of said plasma. This is caused by secondary, primarily mechanical, effects such as rapid expansion of the generated plasma. This effect is very local because, below the threshold, there is zero or very little linear and non-linear absorption while, above the threshold, a plasma is generated which even more strongly absorbs the laser light. In other words, effects such as LIOB only occur in the focal spot, while above and below the focal spot no or very much weaker effects occur. This means that, for example, the epidermis may easily be safeguarded against undesired effects or damage.
Laser skin ablation through a multiphoton ionization process, such as for example laser induced optical breakdown, requires high light intensities of the order of 1013 W/cm2. Due to a very high photon flux (typically >1031 cm−2 s−1), multiple (N) photons with an energy of hv at the wavelength of λ behave like a photon of energy Nhv and interact with an electron to free it from the valence band. This requires the total energy of the absorbed photons to be greater than the ionization potential (Nhv>Δ). The generation of this so-called seed electron or free electron by ionization requires multiple photons (N) having the same polarization confined in space (focal volume) and in time (˜nano to femto seconds) with a total energy exceeding the ionization potential (Nhv>Δ) of the material. Achieving a multiphoton ionization process deep inside the skin is a challenging task.
US2013/0199540 A1 discloses a device for plasma treatment of living tissue, with a plasma source for generating an atmospheric plasma jet, with a support device for a body part comprising the tissue to be treated, with a movement device for moving the plasma source relative to the surface of the tissue, and with a control device for controlling the movement device and for controlling the operation of the plasma source, wherein the control device has means for adjusting the plasma output as a function of the position relative to the tissue. In an embodiment, the device has optical means for measuring a distance between the front end of the outlet opening of the plasma jet and the object to be treated. Said optical means comprise a laser source generating a laser beam which is directed towards the object to be treated through a channel formed in the internal electrode of the plasma generator. The laser beam reflected by the object is directed in opposite direction through the channel and is reflected to a photosensor by means of an output coupling mirror. In another embodiment, before, during and after the plasma treatment a heat treatment, light treatment and/or laser treatment can be carried out. These additional treatments can support and extend the way in which the plasma treatment works.